Epoxides constitute an important class of chemical intermediates useful for the preparation of polyether polyols, glycols, glycol ethers, surfactants, functional fluids, fuel additives and the like. Many different methods for synthesizing epoxides from the corresponding olefins have been described in the literature. A Japanese patent application assigned to the Tosoh Corporation and published in 1992 (Kokai No. 4-352771) proposed making propylene oxide by reacting propylene, hydrogen and oxygen using a catalyst comprising a Group VIII metal and a crystalline titanosilicate. Improvements to or variations of this basic process were subsequently described in the following published patent applications: WO 97/25143, DE 19600709, WO 96/02323, WO 97/47386, WO 97/31711, JP H8-269030, and JP H8-269029.
As with any chemical process, it would be desirable to attain still further improvements in epoxidation methods of this type. In particular, increasing the selectivity to epoxide and extending the useful life of the catalyst would significantly enhance the commercial potential of such methods. Using the reaction conditions and catalysts described in the literature, for example, hydrogenation of the olefin to the corresponding saturated hydrocarbon competes with the desired epoxidation reaction. The discovery of more effective ways of suppressing this side-reaction would be highly advantageous.